1. Field of the Invention
The present invention relates, in general, to tantalum chip capacitors with lead frames and, more particularly, to a tantalum chip capacitor with a cut-grooved anode lead frame designed to allow a tantalum element set in a small-sized resin mold package of the capacitor to have a desired size, thus restricting an increase in impedance of the tantalum chip capacitor regardless of a reduction in the size of the package according to the recent trend of smallness of the tantalum chip capacitors.
2. Description of the Prior Art
As well known to those skilled in the art, tantalum chip capacitors have been widely used in a variety of applied circuits operated, with low rated voltages, in addition to a variety of industrial electronic equipments. Particularly, such tantalum chip capacitors have been preferably used in circuits, the operational performances of which are determined by their frequency characteristics. In the prior art, portable communication equipments typically use such tantalum chip capacitors for accomplishing a noise reduction.
As shown in FIGS. 1 and 2, a conventional tantalum chip capacitor 100 includes a tantalum element 102, which is set in a resin mold package 112 at a predetermined position. A anode lead wire 108 integrally extends from the tantalum element 102, while the inside end of the anode lead frame 104 is welded to the anode lead wire 108 into a single body and extends to the outside of the package 112. The tantalum chip capacitor 100 also has a cathode lead frame 114, wherein its inside end is attached to the tantalum element 102 and its outside end extends to the outside of the package 112. The inside end of the anode lead frame 104 has a straight edge as shown in FIG. 3, so it may be called hereinafter xe2x80x9ca straight lead framexe2x80x9d. The anode lead wire 108 is welded to the straight lead frame 104 through a spot welding process using an electrode welding rod 110 as shown in FIG. 4 after partially overlapping the lead wire 108 on the lead frame 104.
In order to spot-weld the straight lead frame 104 to the anode lead wire 108, it is necessary to make the upper and lower parts of the end of the anode lead wire 108 into flat surfaces. This process is called xe2x80x9cbending processxe2x80x9d and the boundary between the flat surfaces and un-pressed part is called xe2x80x9cbending linexe2x80x9d. Each of the flat surfaces starts at a bending line and is terminated at the end of the lead wire 108, and acts as a contact surface for the welding. The bending line is formed on the anode lead wire 108 by applying pressure to the lead wire 108 before the spot welding process. When the lead frame 104 is welded to the anode lead wire 108, the straight edge of the lead frame 104 is laid on the upper flat surface of the anode lead wire 108 along a welding line, thus defining a welded area starting at the welding line and terminated at the outside end of the lead wire 108. In such a case, the welding line is spaced apart from the bending line by a distance xe2x80x9cLxe2x80x9d as shown in FIGS. 3 and 4. After the lead frame 104 is welded to the lead wire 108 into a single body, an epoxy molding process is performed to form the package 112 enclosing the tantalum element 102, the anode lead wire 108, the anode lead frame 104, and the cathode lead frame 114.
In accordance with the recent trend of compactness and smallness of electronic equipments, it has been necessary to reduce the size of such tantalum chip capacitors. However, in the prior art, such a small-sized tantalum chip capacitor is problematic in that it reduces the size of the tantalum element 102 due to the straight lead frame 104 inevitably occupying substantial space inside the small-sized package 112. When the size of the tantalum element 102 is reduced as described above, the capacitance of the tantalum chip capacitor is reduced. Such a reduction in the capacitance results in an undesirable increase in impedance of the tantalum chip capacitor.
In conventional small-sized tantalum chip capacitors having the straight anode lead frames, it is almost impossible to reduce the size of the straight lead frame. That is, when the straight anode lead frame is reduced in its size in an effort to prevent a reduction in the size of the tantalum element, the package cannot firmly hold the anode lead frame and allows the lead frame to be easily removed from the capacitor. Therefore, the straight anode lead frame must maintain a sufficient size, so the lead frame undesirably occupies substantial space inside the package when the capacitor size is reduced to accomplish the recent trend of smallness of the tantalum chip capacitor.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a tantalum chip capacitor which has a cut-grooved anode lead frame welded to the anode lead wire of a tantalum element at a welded area moved outward from a position of the conventional welded area, thus resulting in the enlargement of the tantalum element size.
Another object of the present invention is to provide a tantalum chip capacitor, which restricts an increase in its impedance regardless of a reduction in the size of its package according to the recent trend of smallness of tantalum chip capacitors, and which thus has improved performance.
In order to accomplish the above objects, the present invention provides a tantalum chip capacitor, comprising: a tantalum element, produced using tantalum oxide as a dielectric substance; an anode lead wire extending outward from a side surface of the tantalum element, and having flat surfaces on the upper and lower surfaces of the end portion thereof; a cathode lead frame the inside end of which is attached to the tantalum element and the outside end of which forms a mounting terminal for surface-mounting the tantalum chip capacitor on a circuit board; an anode lead frame having a cut groove at the center of the inside end thereof, the inside end being welded to the lead wire at the overlapped part of the upper flat surface of the lead wire and the inside end having the cut groove, the outside end forming a mounting terminal for surface-mounting the tantalum chip capacitor on the circuit board; and a mold package enclosing the tantalum element, the lead wire, a part of the cathode lead frame attached to the tantalum element, and a part of the anode lead frame welded to the lead wire.
In the tantalum chip capacitor of this invention, the cut groove may have a V-shaped profile or an arc-shaped profile. In addition, the cut groove has a depth set to 4%xcx9c50% of a reference length which is the length of the part of the anode lead frame enclosed in the package.